Method and material for preventing the tarnishing of silverware



Patented Nov. 15, 1938 PATENT 'Q-FFICE METHOD MATERIAL FOR; PREVENTINGTHE TA RNIS I-IING or. SILVEBWARE Kenneth H. Barnard and Arthur- McLean,A v Mass s nors to P c fi M l s, Lawrence, Mass., a corporation ofMassachusetts N Drawing. Application November 13, 1937,

Serial No. 174,486

4 Claims. (01. Isa-241) ammonia inf-26 Baum. Add water'to make the Thisis an improvement on the method and material patented by Grinnell Jonesof Cambridge, Mass. Patent No. 1,766,646, June 24, 1930, for preventingthe tarnishing of silverware.

The Jones patent described a fabric for protecting silverware fromtarnish comprising a material, suitable for wrapping, impregnated withfinely divided silver, or a compound thereof, which would combine withthe tarnishing gases in the atmosphere and thereby protect the silverwrapped in the protecting material.

The Jones patent describes a fabric impregnated with silver or a silvercompound to protect silver from tarnish. The specific example is darkbrown, very powerful in color and will overpower other dyes and moreoveris somewhat dusty and uses a large amount of silver. Much of it has beenused commercially.

Barnard and Kane Patent No. 2,003,333, June 4, 1935, describes a fabricimpregnated with silver ferrocyanide which is an improvement in variousWays on the dark brown fabric described by Jones. The Barnard and Kanefabric has been successful in commercial use, also.

While the cloth impregnated according to Patent No. 2,003,333 issuccessful in protecting silver and has advantages over Jones dark brownfabric it has the serious disadvantage that a part of the impregnatingmaterial is readily driven off as a dust and thus silver is Wasted andfurthermore, much silver is necessarily wasted in the process ofmanufacture.

Our invention is also an improvement in other Ways over the GrinnellJones invention and the invention of Patent No. 2,003,333.

Our invention, in brief, consists in impregnating the cloth to beprotected with a clear silvercontaining solution soluble in a volatileliquid, as ammonia, which thus permeates the entire cloth. When thevolatile solvent evaporates it precipitates the silver salt in thematerial. In conse quence little or none of the silver salt is lost inthe process of manufacture and little or none of the silver salt is lostas a dust when the fabric is handled.

This principle may be carried out in many ways, of which the followingis an example:

First take five pounds of silver nitrate crystals dissolved in threegallons of water and three and one-half pounds of trisodium phosphatedissolved in three gallons of water; mix the two solutions (which may bedone in tubs). This will precipitate a yellowish white silver phosphate;add enough ammonia to just dissolve this precipitate. This will requireabout one gallon of aquapreviously dyed, with this solution. The squeezerolls of the padder will remove the excessof liquid and the cloth maythen be dried, preferably on a tenter frame in a currentof warm air. Theam-monia evaporates, whereupon the silver phosphate, being insoluble inwater, is precipitated in the cloth in a finely divided state.

We then wash out the sodium nitrate, the other product of the reactionof silver nitrate and trisodium phosphate, in cold water and the clothis thus left impregnated throughout with finely divided silver phosphatein amount corresponding to the strength of the solution used, somewhatyellowish in color, as the protective material. If desired the sodiumnitrate may be washed out of the precipitate before the precipitate isdissolved in ammonia.

If the color of the protective cloth is to be brown, the usual color,the foregoing process is very satisfactory. The protective cloth, ifbeaten, will not give out any substantial amount of dust and the silvergives the protection desired, as stated in the Jones patent.

In some cases, however, the yellow silver triphosphate may beundesirable as, for instance, if a white or light-colored protectivecloth is desired. In such cases we use the same amount of sodiumtetraphosphate (NasPiOia) and proceed as above stated. The silvertetraphosphate is white and will operate substantially as thetriphosphate does.

The cloth used and particularly described in the Jones patent, namelythat precipitated from silver nitrate by sodium carbonate, gives out adust which is wasteful and dirties the hands of the operatives.Ferro-cyanide gives forth even more dust.

Various devices may be used to decrease the amount of dust given orrubbed off from the silver oxide cloth and the silver ferro-cyanidecloth but the cloth impregnated according to the present inventionisvery much better than any way now known to us for diminishing the dustin the silver oxide and the silver ferro-cyanide impregnated cloths.Furthermore, the advantages of having the silver salt precipitatedwithin the fibres of the cloth in the manner shown makes a saving in theamount of silver required as all the silver not taken up by the fabricmay be used again as a part of the liquid used for impregnating a.further batch of cloth.

which the clothis subjected, and the lengthof time protection isdesired.

We have described the use'of ammonia. as the volatile solvent becausethat is, by' far, the simplest solvent which will dissolvethe silver'phosphate or silver tetraphosphate, butan'y suitable volatile solventwhich will dissolve the silvercontaining salt and evaporate quickly toprecipitate it can be used.

Furthermore, our invention is used if 'the. method of impregnating thecloth bysoaking it with a silver-containing material insoluble in water,dissolved in a volatile chemical which will precipitate thesilver-containing salt in the fabric on evaporation is employed.

The word fabric is broadly used to include any kind of cloth, paper orfibrous or cellulosic material.

We claim: 7 V 1. A fabric for protecting silverware from tarnishcomprising a material suitable for-wrapping,

impregnated with a phosphate of silver so associated with the fabric asnot to give forth a dust in material quantities by ordinary handling.

2. A fabric for protecting silverware from tarnish comprising a fibrousmaterial impregnated with silver triphosphate so associated with thefibres as not to give forth a dust in material quantities by ordinaryhandling.

'3. The method of impregnating a fabric with a silver phosphate whichconsists of precipitating a silver phosphate insoluble in water by asuitable phosphate, dissolving the precipitate in aqua ammonia,impregnating the fabric with the dissolved precipitate, allowing theaqua ammonia to evaporate, thus precipitating the silver phosphate inthe fabric and washing out the water soluble chemicals from the fabric.

, 4. The method of impregnating a fabric with a silver salt whichconsists of precipitating a silver saltinsoluble in water by a suitablechemical, dissolving the precipitate in aqua ammonia, impregnating thefabric with the dissolved precipitate, allowing the aqua ammonia to,evaporate, thus precipitating the silver salt in the fabric and washingout the water soluble chemicals from the fabric.

KENNETH H. BARNARD. ARTHUR F. MCLEAN.

